The present invention relates to an optical device, and an optical transceiver and other optical apparatuses using the optical device. For example, the invention relates to optical apparatuses such as an optical transceiver and a dual core/single core converter that are capable of bidirectional optical communication, that is, capable of sending and receiving an optical signal, as well as to an optical device for light wave guidance used in those apparatuses.
With the recent development of high-speed, large-capacity communication networks, communication control equipment, etc., the communication using optical fibers has become the mainstream. For example, such terminals as information appliances provided in homes can send and receive a signal if they are connected to a communication network such as the Internet via optical fibers. Optical fibers are also often used in interconnecting a personal computer, a TV, a DVD player, a video game machine, etc. in a home. For those reasons, less expensive, compact, and highly efficient optical transceivers that can also be used in information appliances etc. are now desired.
Such an optical transceiver is disclosed in Japanese Patent Laid-Open No. 149008/1983, for example. FIG. 1 is a perspective view showing the structure of an optical device 1A that is used in this optical transceiver. The optical device 1A is produced in the following manner. Two mold plates 2 each formed with a Y-shaped groove are laid on each other to form a Y-shaped cavity 3 inside. Transparent resin is poured into the cavity 3 to form a light guide 4.
Where the optical device 1A is used as part of an optical transceiver 1, as shown in FIG. 2, a light input element 5 and a light-receiving element 6 are opposed to the respective branch-side end faces of the light guide 4 and the end face of an optical fiber 7 is opposed to the other end face of the light guide 4. If an optical signal A is output from the light input element 5, the optical signal A enters the light guide 4 through its end face and then irradiates on the optical fiber 7 from the end face of the light guide 4 located on the other side as indicated by solid-line arrows in FIG. 2. On the other hand, if an optical signal B that has traveled through the optical fiber 7 is output from the end face of the optical fiber 7, the optical signal B enters the light guide 4 through its end face and is then received by the light-receiving element 6 located on the other side of the optical device 4 as indicated by broken-line arrows in FIG. 2.
However, in the light guide 4 having the above structure, since there is a light guide portion that is shared by the sending light guide and the receiving light guide, part of the optical signal A that is output from the light input element 5 is reflected by the end face of the light guide 4 and a resulting return optical signal a1 enters the light-receiving element 6 to cause crosstalk. Further, if part of the optical signal A that has been output from the light input element 5, traveled through the light guide 4, and been output from the other end face of the light guide 4 is reflected by the end face of the optical fiber 7, a reflection optical signal a2 returns to the light guide 4 and enters the light-receiving element 6 to also cause crosstalk. If the transmission distance is sufficiently long, a reception light quantity of a primary reception signal can no longer be distinguished from that of crosstalk, which disables bidirectional communication.
In the optical device 1A or an optical transceiver 1 having the above structure, the light guide 4 is formed by pouring transparent resin into the cavity 3 of the mold plates 2. However, it is difficult to register the grooves of the respective mold plates 2 with each other with high accuracy. Further, as the diameter of the cavity 3 decreases, it becomes more difficult to pour transparent resin into the cavity 3; that is, it becomes more difficult to produce the optical device 1A with high accuracy.
Japanese Patent Laid-Open No. 2000-162455 discloses an optical transceiver capable of preventing crosstalk. As shown in FIG. 3, in this optical transceiver 8, a sending light guide 10 and a receiving light guide 11 are provided on the surface of a silicon substrate 9. To prevent crosstalk, a groove (gap) 12 is formed between the light guides 10 and 11.
However, in the optical transceiver 8 having the above structure, since the sending light guide 10 and the receiving light guide 11 are formed on the silicon substrate 9 by using a semiconductor manufacturing process, complex manufacturing steps are needed and the manufacturing cost becomes high. Further, it is difficult to form thick light guides 10 and 11 and hence their end faces to be opposed to an optical fiber 3 cannot obtain large areas, resulting in low efficiency of light utilization.